conversion mg/Nm3 to PPM 1

[yulinios]

Hi to Everybody

I would like to know how to convert mg/Nm3 to PPM for a flue gas of coal boiler, the analizer in flue gases indicates +/-1200 mg/Nm3 SO2 at -0.28 KPa and 135°C.

Bye There

 

[25362]

SO2 has a density of 2.9268 mg/mL at NTP (0 deg C, 1 atm). Thus, 1200 mg would have a volume of 1200/2.9268 = 410 mL.

410 mL/m³ = 410 ppm (v/v)​

Since the gases are considered ideal, the given operating conditions wouldn't affect this result.

 

[Fizzhead]

yulinios:

One thing to clarify here. The analyzer indicates +/- 1,200 mg/Nm3. This is at standard conditions and the temperature and pressure conditions cited are merely the characterization of the environment the analyzer is sampling. I believe this is part of what 25362 means by his last statement, but I thought it could bear repeating and a little clarification. The theoretical equation is

(mg/m3)*(1/(1000*MW))*(0.0224m3/mol)= m3 of gas A/m3 of gas mixture

Where mg/m3 is the measured concentration from the analyzer, MW is the molecular weight of the chemical in question in grams/mol and 0.0224 is the volume of a single mole of an ideal gas at standard conditions (i.e., 0C and 1 atm.). The result of this calculation is cubic meters of the particular chemical species of interest per cubic meter of mixed gas. To convert to ppm, multiply the result by 10^6. Thus the final equation is:

(mg/m3)*(22.4/MW)= PPM or 1,200*(22.4/64.06) = 420 ppm

It appears the difference here between my result and 25362's is that I calculate a pure vapor phase density of 2.860 mg/ml, not the quantity used by 25362. I would expect this is a tabulated value based on laboratory results and is representative of the error introduced by the ideal gas assumption.

 

[25362]

To Fizzhead, you guessed right. The density was taken from Perry VI Table 3-30. I prefer to use tabulated NTP or STP data, whenever available, as in the case of SO2, rather than using the ideal gas law's 22.4 m³/mol.

In this manner errors, especially for gaseous molecules composed of several atoms, are minimized.